In a light-emitting device described in Patent Literature 1, light obtained by coupling light from a plurality of light sources is incident to a light-receiving device such as an optical fiber and thus a high output is obtained. In such a light-emitting device, light emitting diodes (LED), semiconductor lasers, or the like are used as light sources, and the light from the light sources is coupled using a lens or a prism.
[Patent Literature 1] Japanese Patent No. 3228098